1. Field of the Invention
The present invention relates to a laminate type LC element and particularly to a laminate type LC element that comprises a laminated insulator and an LC circuit including inductors and capacitors, the LC circuit being formed in the laminated insulator to provide a distributed constant.
2. Description of the Related Art
With the development of the electronic techniques, many electronic circuits are currently utilized in various fields. It is thus desirable that these electronic circuits can operate stably and reliably without the effects of any external noises.
Various high-performance electronic instruments are increasingly subjected to severe limitations against noise. It is desired to provide a small-sized and high-performance noise filter capable of reliably eliminating noises.
FIG. 21 shows an LC noise filter constructed in accordance with the prior art, which comprises a core 1 and two windings 2 and 3. Each of the windings 2 and 3 is connected, at each end, parallel to the corresponding end of the other windings through a capacitor 4 or 5.
In such an arrangement, an inductor consisting of the core 1 and the windings 2, 3 is increased in size. And yet, such an inductor must be formed separately from the capacitors 4 and 5. This results in an increased in cost and size of the entire filter system.
Many proposals intending to overcome the above problems have been made, for example, in Japanese Patent Laid-Open Nos. Sho 56-50507, Sho 56-144524, Sho 56-142622 and Sho 63-76313.
FIG. 22 shows a composite electronic part constructed in accordance with Japanese Patent Laid-Open No. Sho 56-50507, in which a laminate is formed by stacking a plurality of insulator layers 10a, 10b, 10c. A conductive pattern 12a, 12b or 12c is located between the adjacent insulator layers to wind and extend continuously from one layer to another layer. In such a manner, there is formed a coil L having a predetermined number of turns.
A conductive layer 14a or 14b is also disposed between the adjacent insulating layers (10a and 10b; 10b and 10c) and spaced away from the corresponding conductive pattern 12a or 12c. A capacitance C is formed between each of the conductive layers 14a and 14b and the corresponding conductive pattern 12a or 12c.
In such a manner, there is provided a lumped-constant type noise filter including inductance L and capacitance C as shown in FIG. 23. Such a noise filter can be used as a small-sized and lightweight LC noise filter since inductance L and capacitance C are incorporated into the laminate.
This LC noise filter can have only a very small capacitance C between the coil and the conductive layers 14 since the conductive layers 14a and 14c forming the capacitance are located adjacent to the linear portions of the conductive patterns 12a and 12c forming the coil. Thus, the LC noise filter does not provide a good noise attenuation.
This lumped-constant type LC filter cannot reliably remove various noises and particularly common mode noises as on switching surge or normal mode noises as on a ripple.
In addition, this LC filter can be used only as a three-terminal type normal mode filter, rather than a four-terminal type common mode filter.